Chiptune music player featuring SN76489 and ATtiny861/ATtiny84
This project grew out of a Wikipedia surfing session. In reading about the computers of my childhood, I came across an article about the TI SN76489 sound chip, used by two of the machines I used as a kid (the TI 99/4A and IBM PCjr). I wondered if you can readily buy this IC, and if you can talk to it reasonably easily with modern hardware. The answer to both questions is yes!
All eight pins of PORTA are connected to the SN76489's data lines. PB4 connects to /WE and latches a value to the chip. PB5 (CLKO) outputs the ATtiny861's clock signal directly to the sound chip's clock input. /OE is permanently tied low and READY is ignored. I'm not sharing a bus with anything else...
The MCU firmware plays music from an array of bytes stored in program memory (in songs.c). It's a very simple binary format with three one-byte commands that play a note, play a noise, and sleep. To keep things simple, I ignore note-off events and simply make each note decay at a constant linear rate after it is struck. Much like an actual music box!
util/process_midi_file.cpp will take a MIDI file and output a set of arrays for songs.c. It makes use of light-midi-parser as a submodule.
This project can also be built for the ATtiny84, via make -e DEVICE=attiny84.
With this target there will be just one blinking light, rather than one per channel. See main.c for wiring differences.
I've also created a more elaborate stereo two-chip player using the Raspberry Pi Pico, pico-player.